由(x+y)²=1
x+y=±1,
由(x-y)²=49,
x-y=±7
(1)(x+y)²+(x-y)²=1+49
∴2x²+2y²=50,
即x²+y²=25.
(2)(x+y)²-(x-y)²=1-49
4xy=-48,即xy=-12.